Blocq's disease

Did You Know?

• Primary motor cortex neurons may control skill acquisition and retention through plasticity from movement repetition.
• Leg braces and in-shoe splints can help maintain proper foot alignment for standing and walking.
• Bowling shoes with upturned toes can reduce stumbling.

Descending motor pathways

The vestibulospinal tracts are crucial for postural adjustments, head movements, and balance maintenance. The lateral vestibulospinal tract excites antigravity muscles to compensate for body tilts, while the medial vestibulospinal tract stabilizes head position. The reticulospinal tracts connect the corticospinal system to regulate flexor responses and contain circuitry for complex actions like orienting and maintaining posture. Commands initiating locomotor circuits in the spinal cord are transmitted through the medullary reticulospinal tract, integrating sensory input to guide motor output.

Pathology

The deficit in Blocq's disease appears localized in the putamen and globus pallidus, reducing muscle force at movement initiation. Initiation of stepping involves reticulospinal and vestibulospinal projections in ventromedial descending brainstem pathways, modulated by connections with the cerebral vermis. Most patients exhibit a hypokinetic gait disorder due to dysfunction in basal ganglia, frontal lobe, and brainstem circuitry, leading to a wide-based or variable stance and truncal imbalance. Psychogenic tremor involves the temporoparietal junction, where hypoactivation during functional tremor episodes may represent a failure to match actual and predicted sensory feedback, inhibiting movement. Additionally, abnormally strong amygdala–supplementary motor area connectivity and weak supplementary motor area–prefrontal cortex connectivity have been observed, suggesting a lack of appropriate prediction outcome signal for the conversion tremor.

Brain affected areas

The basal ganglia, including the striatum, globus pallidus, substantia nigra, and subthalamic nucleus, are associated with voluntary motor control and action selection. The striatum, the major input station, receives input from the cerebral cortex. The dorsal striatum, comprising the putamen and caudate nucleus, contributes to action selection and initiation under dopamine influence. The putamen and globus pallidus form the lenticular nucleus; the globus pallidus sends inhibitory output to the thalamus and midbrain, affecting posture control. Excitation of the globus pallidus interior by the subthalamus facilitates movement suppression, while disinhibition via striatal inhibition of the globus pallidus enables movement initiation. The ventral striatum is associated with emotional and motivational aspects of behavior, innervated by dopaminergic fibers from the ventral tegmental area.

Diagnosis

Diagnosis involves a medical history review and a neurological examination including gait evaluation. The doctor may observe stance, posture, base width, gait initiation, walking speed, stride length, step height, foot clearance, continuity, symmetry, trunk sway, path deviation, arm swing, involuntary movements, turning ability, and rising from a chair. Chair testing may involve propelling a swivel chair forward and backward.